Electrical apparatus



Filed Dec. 24. 1927 2 Sheets-Sheet 1 Fay. Z

INVENTOR. dqgrcy 4e B 1' M 1932- P. LE B. SPENCER ELECTRICAL APPARATUSFiled Dec. 24, 1927 2 Sheets-Sheet 2 Fly 2 IN V EN TOR. @1213; Le a/w-Sher Patented Oct. 25, 1932 PERCY LE BARON SPENCER, OI MEDFOBD, MASSAGEU'SETTB ELECTRICAL APPARATUS Application filed December 24, 1827.Serial No. 242,309.

The present invention relates to electrodynamic loud speakers and inparticular to loud speakers in which the diaphra m or radiating elementis moved by the e ectric forces created in the electrodynamic mechanismin both forward and reverse directions without the intervention ofrestoring forces supplied by springs or the like.

Loud speakers having electrodynamic driv- .ing or operating mechanismare known in the art. One kind of loud speaker of this type has anelectrodynamic drive comprising a ma etic field set up between twoconcentric cylmdrical magnets in which is situated a cylindrical coilcarrying the alternating or speech current. When the current in thealternating coil is in one direction the coil moves one way and when thecurrent is in the oppo site direction the coil moves in the reverse 2direction. This device while successfully used has certain objections.The coil must furnish the mechanical force to move the sound radiatingmember and must therefore be strong enough to withstand the mechanical gvibrations and still keep together. It must also be stiff enough to havepractically no frictional mechanical losses. In addition to this toallow sufficient room for the coil to move up and down without coming incontact with the cylindrical pole pieces, the air gap must be wider thanthe coil whichapprecia 1y builds up the field current necessary toenergize the air gap.

Another type of electrodynamic drive which may be employed in loudspeakers is somewhat similar to that described above. In this type ofdrive the speech or alternating current is not conducted directly to amoving coil but is induced therein by means of a transformer. In somedrives of this type both primary and secondary of the transformer are inthe magnetic field, the primary being stationary however, and thesecondary moveable and operating the sound radiating member. Where theprimary and secondary are in the magnetic field a larger air gap isrequired when both the primary and secondary are situated therein thanin the type Just previously mentioned. The advantage of 50 placing bothprimary and secondary in the air gap of the magnetic field-is reatestwhere a magnetic circuit is employe having two coaxial cylindrical airgaps. In this case the primary can be wound upon the core in oppositedirections in order to do away with induc tive effects in the electriccircuit and the secondary will therefore have current induced inopposite directions in both halves thereof. As has been pointed outabove however, this system has its disadvantages in that the air gap islarge necessitating both greater excitation in the direct current fieldand in the movin coil than is uite often desirable.

n the present invention all these difliculties have been overcome by theconstruction of the secondary of the transformer or the moving elementin such a manner that there is no need of placing the primary in themagnetic field of the electrodynamic system of the loud speaker, but onthe other hand, it can be entirely removed therefrom. In addition tothis the construction of the secondary is such that in itself it ispractically noninductive and furnishes therefore no out of placecomponent which cuts down the efficiency and capacity of the loudspeaker in addition to causing distortion because of differentreactances at different frequencies. These advantages and other featuresand objects of the present invention will be explained more fully in thedescription of the embodiment shown in the annexed drawings, in which:

Figure 1 shows a sectional view through the center of the speaker.

Figure 2 shows a detail of an element of the speaker.

Figure 3 shows the element shown in Figure 2 after construction. 7

Figure 4 shows an end view of Figure 3 and Figure 5 shows a furtherdetail.

In Figure 1, 1 and 3 are cylindrical soft iron pieces machined orpressed to the shape indicated in the drawings so that any sectionthrough them in the manner indicated in Figure 1 form a U shaped magnet26 with the pole faces 22 and 23 as close together as the constructionwill ordinarily allow. The pieces 1 and 3 have broad flanges 24 and 25to provide a large surface area in order that the reluctance of themagnetic path across it .100

will be as low as possible and also to provide a large clamping surfacefor the machine screws 4 to hold the two halves of the magnet securelytogether and to the frame or case 5.

The magnet 26 is constructed in this manner so that the coil 2 may beprewound and placed within the space between the two arms of the magnetwhich are then clamped together. JVithin the cylindrical opening, leftopen by the poles 22 and 23 of the magnet 26, is situated a copper,silver, or other kind of conducting element 27, which will be accuratelydescribed later, and within this conducting element 27 is a soft ironcore 28. The soft iron core 28 is held in place by a non magnetic andpreferably non conductive plate 29 through the centre of which passes astud or bolt 30, supporting the core 28 firmly in place.

The path of the direct current flux obtained by direct currentexcitation of the coil 2 is, let us say, from the north pole 22 acrossthe air gap adjacent thereto across the conducting element 27 to thecore 28 and back in reverse direction to the south pole 23. In the upperair gap 31 the flux flows towards the core and in the lower air gap 32the flux away from the core. If therefore the current is made to move inthe conducting element in the upper part in one direction and in thelower part in the opposite direction, the forces acting on theconducting element Wlll make it move in the same direction.

The conducting element is shown alone in Figure 3 and comprises a flatrectangular portion 33 connected to a neck conducting element 16 whichis connected to a circular lower portion 34 divided into two parts bythe opening 36. Through the opening 35 1s placed a laminated iron coreshown as 18 in Figure 1. The current induced in the winding 33 which inthe present case is a single turn but may be more in other cases, flowsthrough one side of the neck 16 to the upper part of the circular ortion34, artly around this portion an then to t e lower ortion, and aroundthis when it returns bac to the rest of the upper portion and to theother side of the conducting neck 16. The direction of the current inone instance is shown b the arrows 37 from which it will be note thatthe current in the u per part of the circular portion 34 always ows inthe opposite direction from the lower portion.

A development of the conducting element is shown in Figure 2 from whichit will be noted that it is stamped out of a single piece of material inflat form and comprises simply the two flat portions 33 and 34 joined bya fiat neck 16. It should also be noted that a. T shaped slot 38 isprovided running from the open center 35. This T slot forms the openingbetween the opposite halves of the neck 16 and the opening 36 of Figure3.

As will be noted from above, due to the half of the circularportion 34provides withv out the need of a primary in the magnetic field, thenecessary polarity of current in the oppositely flowing magnetic fieldsof the two air gaps to produce forces driving the conductor in the samedirection.

At one end of the conducting element, are the fingers 39 to which isfastened firmly the sound radiating element 21 by shellac or othersuitable means. The radiating element in the present case is a cone, atthe edge of which is fastened a soft leather or chamois strip which laysover the edge or flange 19 of the case 5. Across and within the neck ofthe cone is a fiat disc 40 which is firmly attached at its edges to theWall of the cone.

Through the center of this disc passes the stud or bolt 30 which hasalready been mentioned above. The cone 21 is freely supported by meansof the flexible edge 20 and the bolt 30 through the paper disc 40, sothat whatever position the cone is placed in by motion of the conductingelement, no restoring force is exerted in opposition and therefore noresonance effect due to the period of such a restoring force as forinstance from the use of springs is present in the device.

Instead of the present method of support, the cone may be suspended bcords at various points or the cone may be entirely free and theconducting element suspended by flexible cords from the fingers 39 andfrom the neck 16. Either or any method of suspension may be used whichwill not hamper the free motion of the moving element.

The transformer for the conducting element is contained entirely withinthe unit and is supported by the brace 41 held fast to the magnet 26 bythe screws 42.

The primary of the transformer consists of a w1nding 17 having a greatnumber of turns and the secondary element already discussed. Both ofthese windings have a common closed core 18- The speech current isconducted to the winding 17 by means of the leads 12 and 15 whichconnect with the connecting studs 8 and 11 on the plate 43 of the case7, fastened in turn by screws 6 to the magnet 1. The excitation for thedirect current field is supplied by means of the leads 13 and 14 whichconnect to the conducting studs 9 and 10.

The operation of the device should be obvious from the explanation anddescription given above. The principle of the operation conductor tomove it in a direction perpendicular to the direction of the flux, oneway if the current is flowing one way in the wire and the opposite wayif the current is flowing oppositely in the wire.

In the present case the speech current induced in the conducting elementalways flows in opposite directions in the opposite halves thereof, butthe flux also always flows in opposite directions across the oppositehalves of the element. The forces therefore at any instant always worktogether. When the current flows one way the conducting element isforced in one direction and when it flows the other way it is urged inthe other direction.

The commercial advantages of the present construction over the priorart, are great not only in the production of a loud speaker which willreproduce without distortion because of the elimination of varyingreactance to different frequencies, but also in the pro duction of aloud speaker at a very reasonable cost because of the elimination of theprimary element from the magnetic field and the elimination of carefulmachining to obtain a small air gap. v

The fact that a small air gap can be obtained with little diflicultyalso means that a highly efiicient instrument can be obtained and that amaximum response will be given for the amount of energy supplied to theapparatus. Further due to the fact that the conducting element issubstantially non inductive there will be no electrical resonance effecteither in the primary or secondary of the transformer or in the speakeritself. The added advantage that eddy current losses are practicallyeliminated without the use of a laminated core or magnet is possiblebecause oft-he fact that the oppositelyconducting parts of theconducting element always make the varying magnetic forces in themagnetic circuit zero. The magnetizing force in the core due to theupper half of the conducting element is always compensated completelyand accurately by the magnetizing force due to the lower half of theconducting element. This is possible because of the noninductivecharacter of the moving element.

The above description and drawings show one form of my invention. I donot wish to limit my invention however to this form only for theinvention may take other embodiments substantially equivalent andoperating in the same manner as the embodiment above described.

Having now described my invention, I claim 1. A loud speaker comprisinga core of magnetizable material, outer surrounding pole pieces and meansfor setting up magnetic fields between said core and said pole pieces,the flux in adjacent fields flowing to and. from the core, a conductivemember having elements substantially surrounding said core but notcompleting a conductive turn about the same, the elements being situatedin adjacent fields and the current flowing in oppofields, currentconductive means positioned in said magnetic field and having conductiveelements substantially surrounding but turned back upon themselves insuch a fashion that there is no inductive effect with said core itself,the current in said elements in adjacent fields flowing in oppositedirections, a sound radiating member attached at one end of saidconductive member and means for conducting speech current to saidconducting member.

3. A loud speaker comprising a core of magnetizable material, a shellshaped magnet surrounding said core and forming a plurality of magneticair gaps between said core and shell, current conductive meanspositioned in said air gaps and substantially surrounding but turnedback upon itself in such a fashion that there is no inductive effectwith said core, the current flowing in said conductive means beingdirected to produce additive mechanical forces, a sound radiating meansattached to said conductive member and means for impressing speechcurrent on said conductive member.

4. A loud speaker comprising electromag netic means forming circularmagnetic air gaps,substantially aligned current conducting meanspositioned concentrically in said air gap, but not electrically linkingthe flux in the core which is substantially within the enclosure of theconductor, the current flowing in said conductor causing the mechanicalforces to add a sound radiating member attached to said conductor andmeans for impressing speech current on said conductor.

5. In an electrodynamic loud speaker acurrent conducting element havingat least one turn with its longer sides disposed parallel to each otherand formed to have each side make substantially, but not completely, aclosed loop.

6. An electrodynamic loud speaker, comprising clectromagnetic meanshaving a central core, a plurality of magnetic members surrounding butspaced from said core, forming a plurality of air gaps therebetween, acurrent conducting member having at least one completed turn with longersides disposed parallel to each other and formed to have each said si demake substantially,but not completely, a closed loop fitting in said airgaps, a sound radiatin element connected to said conducting mem er andmeans to impress current upon said conducting member.

7. An electrodynamic loud speaker com- 5 prising electrodynamic meansforming a plurality of aligned circular air gaps, a current conductingmember having at least one completed turn, including two long sidesdisposed parallel to each other and formed to have each side makesubstantially but not com-. pletely a circle, located in separate airgaps. a sound radiating element connected to said conducting member andmeans to impress current upon said conducting member. 8. In anelectrodynamic loud speaker a cur rent conducting element formed of aflat piece of conducting material of substantially T shape and havingstamped out from within a substantially similar T shaped figure form--ing a continuous conducting loop about the margin of the inner T, thetop of said T being formed to make a substantially, but not completelyclosed loop.

9. In an electrodynamic loud speaker, a current conducting elementforming a closed turn having two substantially parallel long sides, saidlong sides being formed in a substantially but not completely closedcircle.

10. In an electrodynamic loud speaker a current conducting elementforming a closed turn having two substantially parallel long sides, saidlong sides being formed in a substantially but not completely closedcircle, a plurality of fingers rovided on one of said "3 long sides, anda radiating element mounted against said fingers.

PERCY LE BARON SPENCER.

